/*
 * Copyright 2002-2014 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.bangcommunity.bbframe.common.utils.reflect;

import java.beans.BeanInfo;
import java.beans.IntrospectionException;
import java.beans.Introspector;
import java.beans.PropertyDescriptor;
import java.util.Collections;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.bangcommunity.bbframe.common.utils.lang.ConcurrentReferenceHashMap;
import com.bangcommunity.bbframe.common.utils.lang.StringUtils;

/**
 * Internal class that caches JavaBeans {@link PropertyDescriptor} information for a Java class. Not
 * intended for direct use by application code.
 *
 * <p>
 * Necessary for own caching of descriptors within the application's ClassLoader, rather than rely
 * on the JDK's system-wide BeanInfo cache (in order to avoid leaks on ClassLoader shutdown).
 *
 * <p>
 * Information is cached statically, so we don't need to create new objects of this class for every
 * JavaBean we manipulate. Hence, this class implements the factory design pattern, using a private
 * constructor and a static {@link #forClass(Class)} factory method to obtain instances.
 *
 * <p>
 * Note that for caching to work effectively, some preconditions need to be met: Prefer an
 * arrangement where the Spring jars live in the same ClassLoader as the application classes, which
 * allows for clean caching along with the application's lifecycle in any case. For a web
 * application, consider declaring a local
 * {@link org.springframework.web.util.IntrospectorCleanupListener} in {@code web.xml} in case of a
 * multi-ClassLoader layout, which will allow for effective caching as well.
 *
 * <p>
 * In case of a non-clean ClassLoader arrangement without a cleanup listener having been set up,
 * this class will fall back to a weak-reference-based caching model that recreates much-requested
 * entries every time the garbage collector removed them. In such a scenario, consider the
 * {@link #IGNORE_BEANINFO_PROPERTY_NAME} system property.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @since 05 May 2001
 * @see #acceptClassLoader(ClassLoader)
 * @see #clearClassLoader(ClassLoader)
 * @see #forClass(Class)
 */
public class CachedIntrospectionResults {

    private static final boolean shouldIntrospectorIgnoreBeaninfoClasses = false;

    /** Stores the BeanInfoFactory instances */

    private static final Logger logger = LoggerFactory.getLogger(CachedIntrospectionResults.class);

    /**
     * Set of ClassLoaders that this CachedIntrospectionResults class will always accept classes
     * from, even if the classes do not qualify as cache-safe.
     */
    static final Set<ClassLoader> acceptedClassLoaders = Collections
            .newSetFromMap(new ConcurrentHashMap<ClassLoader, Boolean>(16));

    /**
     * Map keyed by Class containing CachedIntrospectionResults, strongly held. This variant is
     * being used for cache-safe bean classes.
     */
    static final ConcurrentMap<Class<?>, CachedIntrospectionResults> strongClassCache = new ConcurrentHashMap<Class<?>, CachedIntrospectionResults>(
            64);

    /**
     * Map keyed by Class containing CachedIntrospectionResults, softly held. This variant is being
     * used for non-cache-safe bean classes.
     */
    static final ConcurrentMap<Class<?>, CachedIntrospectionResults> softClassCache = new ConcurrentReferenceHashMap<Class<?>, CachedIntrospectionResults>(
            64);

    /**
     * Accept the given ClassLoader as cache-safe, even if its classes would not qualify as
     * cache-safe in this CachedIntrospectionResults class.
     * <p>
     * This configuration method is only relevant in scenarios where the Spring classes reside in a
     * 'common' ClassLoader (e.g. the system ClassLoader) whose lifecycle is not coupled to the
     * application. In such a scenario, CachedIntrospectionResults would by default not cache any of
     * the application's classes, since they would create a leak in the common ClassLoader.
     * <p>
     * Any {@code acceptClassLoader} call at application startup should be paired with a
     * {@link #clearClassLoader} call at application shutdown.
     * 
     * @param classLoader
     *            the ClassLoader to accept
     */
    public static void acceptClassLoader(ClassLoader classLoader) {
        if (classLoader != null) {
            acceptedClassLoaders.add(classLoader);
        }
    }

    /**
     * Clear the introspection cache for the given ClassLoader, removing the introspection results
     * for all classes underneath that ClassLoader, and removing the ClassLoader (and its children)
     * from the acceptance list.
     * 
     * @param classLoader
     *            the ClassLoader to clear the cache for
     */
    public static void clearClassLoader(ClassLoader classLoader) {
        for (Iterator<ClassLoader> it = acceptedClassLoaders.iterator(); it.hasNext();) {
            ClassLoader registeredLoader = it.next();
            if (isUnderneathClassLoader(registeredLoader, classLoader)) {
                it.remove();
            }
        }
        for (Iterator<Class<?>> it = strongClassCache.keySet().iterator(); it.hasNext();) {
            Class<?> beanClass = it.next();
            if (isUnderneathClassLoader(beanClass.getClassLoader(), classLoader)) {
                it.remove();
            }
        }
        for (Iterator<Class<?>> it = softClassCache.keySet().iterator(); it.hasNext();) {
            Class<?> beanClass = it.next();
            if (isUnderneathClassLoader(beanClass.getClassLoader(), classLoader)) {
                it.remove();
            }
        }
    }

    /**
     * Create CachedIntrospectionResults for the given bean class.
     * 
     * @param beanClass
     *            the bean class to analyze
     * @return the corresponding CachedIntrospectionResults
     * @throws BeansException
     *             in case of introspection failure
     */
    @SuppressWarnings("unchecked")
    static CachedIntrospectionResults forClass(Class<?> beanClass) throws BeansException {
        CachedIntrospectionResults results = strongClassCache.get(beanClass);
        if (results != null) {
            return results;
        }
        results = softClassCache.get(beanClass);
        if (results != null) {
            return results;
        }

        results = new CachedIntrospectionResults(beanClass);
        ConcurrentMap<Class<?>, CachedIntrospectionResults> classCacheToUse;

        if (ClassUtils.isCacheSafe(beanClass, CachedIntrospectionResults.class.getClassLoader())
                || isClassLoaderAccepted(beanClass.getClassLoader())) {
            classCacheToUse = strongClassCache;
        } else {
            if (logger.isDebugEnabled()) {
                logger.debug("Not strongly caching class [" + beanClass.getName() + "] because it is not cache-safe");
            }
            classCacheToUse = softClassCache;
        }

        CachedIntrospectionResults existing = classCacheToUse.putIfAbsent(beanClass, results);
        return (existing != null ? existing : results);
    }

    /**
     * Check whether this CachedIntrospectionResults class is configured to accept the given
     * ClassLoader.
     * 
     * @param classLoader
     *            the ClassLoader to check
     * @return whether the given ClassLoader is accepted
     * @see #acceptClassLoader
     */
    private static boolean isClassLoaderAccepted(ClassLoader classLoader) {
        for (ClassLoader acceptedLoader : acceptedClassLoaders) {
            if (isUnderneathClassLoader(classLoader, acceptedLoader)) {
                return true;
            }
        }
        return false;
    }

    /**
     * Check whether the given ClassLoader is underneath the given parent, that is, whether the
     * parent is within the candidate's hierarchy.
     * 
     * @param candidate
     *            the candidate ClassLoader to check
     * @param parent
     *            the parent ClassLoader to check for
     */
    private static boolean isUnderneathClassLoader(ClassLoader candidate, ClassLoader parent) {
        if (candidate == parent) {
            return true;
        }
        if (candidate == null) {
            return false;
        }
        ClassLoader classLoaderToCheck = candidate;
        while (classLoaderToCheck != null) {
            classLoaderToCheck = classLoaderToCheck.getParent();
            if (classLoaderToCheck == parent) {
                return true;
            }
        }
        return false;
    }

    /** The BeanInfo object for the introspected bean class */
    private final BeanInfo beanInfo;

    /** PropertyDescriptor objects keyed by property name String */
    private final Map<String, PropertyDescriptor> propertyDescriptorCache;

    /** TypeDescriptor objects keyed by PropertyDescriptor */
    private final ConcurrentMap<PropertyDescriptor, TypeDescriptor> typeDescriptorCache;

    /**
     * Create a new CachedIntrospectionResults instance for the given class.
     * 
     * @param beanClass
     *            the bean class to analyze
     * @throws BeansException
     *             in case of introspection failure
     */
    private CachedIntrospectionResults(Class<?> beanClass) throws BeansException {
        try {
            if (logger.isTraceEnabled()) {
                logger.trace("Getting BeanInfo for class [" + beanClass.getName() + "]");
            }

            BeanInfo beanInfo = (shouldIntrospectorIgnoreBeaninfoClasses
                    ? Introspector.getBeanInfo(beanClass, Introspector.IGNORE_ALL_BEANINFO)
                    : Introspector.getBeanInfo(beanClass));
            this.beanInfo = beanInfo;

            if (logger.isTraceEnabled()) {
                logger.trace("Caching PropertyDescriptors for class [" + beanClass.getName() + "]");
            }
            this.propertyDescriptorCache = new LinkedHashMap<String, PropertyDescriptor>();

            // This call is slow so we do it once.
            PropertyDescriptor[] pds = this.beanInfo.getPropertyDescriptors();
            for (PropertyDescriptor pd : pds) {
                if (Class.class.equals(beanClass)
                        && ("classLoader".equals(pd.getName()) || "protectionDomain".equals(pd.getName()))) {
                    // Ignore Class.getClassLoader() and getProtectionDomain() methods - nobody
                    // needs to bind to those
                    continue;
                }
                if (logger.isTraceEnabled()) {
                    logger.trace("Found bean property '" + pd.getName() + "'"
                            + (pd.getPropertyType() != null ? " of type [" + pd.getPropertyType().getName() + "]" : "")
                            + (pd.getPropertyEditorClass() != null
                                    ? "; editor [" + pd.getPropertyEditorClass().getName() + "]" : ""));
                }
                pd = buildGenericTypeAwarePropertyDescriptor(beanClass, pd);
                this.propertyDescriptorCache.put(pd.getName(), pd);
            }

            this.typeDescriptorCache = new ConcurrentReferenceHashMap<PropertyDescriptor, TypeDescriptor>();
        } catch (IntrospectionException ex) {
            throw new FatalBeanException("Failed to obtain BeanInfo for class [" + beanClass.getName() + "]", ex);
        }
    }

    BeanInfo getBeanInfo() {
        return this.beanInfo;
    }

    Class<?> getBeanClass() {
        return this.beanInfo.getBeanDescriptor().getBeanClass();
    }

    PropertyDescriptor getPropertyDescriptor(String name) {
        PropertyDescriptor pd = this.propertyDescriptorCache.get(name);
        if (pd == null && StringUtils.hasLength(name)) {
            // Same lenient fallback checking as in PropertyTypeDescriptor...
            pd = this.propertyDescriptorCache.get(name.substring(0, 1).toLowerCase() + name.substring(1));
            if (pd == null) {
                pd = this.propertyDescriptorCache.get(name.substring(0, 1).toUpperCase() + name.substring(1));
            }
        }
        return (pd == null || pd instanceof GenericTypeAwarePropertyDescriptor ? pd
                : buildGenericTypeAwarePropertyDescriptor(getBeanClass(), pd));
    }

    PropertyDescriptor[] getPropertyDescriptors() {
        PropertyDescriptor[] pds = new PropertyDescriptor[this.propertyDescriptorCache.size()];
        int i = 0;
        for (PropertyDescriptor pd : this.propertyDescriptorCache.values()) {
            pds[i] = (pd instanceof GenericTypeAwarePropertyDescriptor ? pd
                    : buildGenericTypeAwarePropertyDescriptor(getBeanClass(), pd));
            i++;
        }
        return pds;
    }

    private PropertyDescriptor buildGenericTypeAwarePropertyDescriptor(Class<?> beanClass, PropertyDescriptor pd) {
        try {
            return new GenericTypeAwarePropertyDescriptor(beanClass, pd.getName(), pd.getReadMethod(),
                    pd.getWriteMethod(), pd.getPropertyEditorClass());
        } catch (IntrospectionException ex) {
            throw new FatalBeanException("Failed to re-introspect class [" + beanClass.getName() + "]", ex);
        }
    }

    TypeDescriptor addTypeDescriptor(PropertyDescriptor pd, TypeDescriptor td) {
        TypeDescriptor existing = this.typeDescriptorCache.putIfAbsent(pd, td);
        return (existing != null ? existing : td);
    }

    TypeDescriptor getTypeDescriptor(PropertyDescriptor pd) {
        return this.typeDescriptorCache.get(pd);
    }

}
